Storage battery having grids consisting of lead, calcium, and tin

ABSTRACT

This invention relates to a battery which is highly resistant to the electrolytic decomposition of electrolyte during equilibrium constant voltage charging. These batteries are distinguished by a grid alloy containing a small amount of calcium and functionally no antimony.

' l mte States Patent 11 1 3,639,175 Marsh I 1 Feb. 1, 1072 ADDITIVES FOR DRY CHARGED References Cited BATTERIES UNITED STATES PATENTS [72] lnventor: Frederick L. Marsh, Minneapolis, Minn.

1,748,485 2/1930 Kugel 136/154 [73] Assignee: Gould-National Batteries, Inc., Saint Paul, 3,011,007 11/1961 Evers etal 136/154 XR Minn. 3.447.969 6/1969 Tudor etal 136/154 XR [22] Filed: July 2,1969 Primary Examiner-Donald L. Walton A ttorneys- Stryker and Jacobson [2]] Appl.No.:838,693

[57] ABSTRACT [52] U.S. Cl 136/154,

156,157,161 A container having a zirconium affording substance that 51] m. Cl ll-l0lm 9 00, is s p activation y water precipitate the p HOl 39/04 phates o t t to the electrolyte fornaet l from the activation of a [58] Field of Search 136/154, water activatablc, boron phosphate slll ihuric acid gel used in a dry charged battery.

4 Claims, N0 Drawing Figs.

ADHITWES FOR DRY CHARGED BATTERIES BACKGROUND OF THE INVENTION Field ofthe Invention This invention relates generally to immobilized electrolytes for secondary cells and, more particularly, to an additive to sulphuric acid boron phosphate gels that precipitates the phosphate from the electrolyte after activation.

Description of the Prior Art eliminate syneresis effectsF-THis ty p 6f have superior ciualit ies ih r e tai ning the sulphuric acid in an immobilized state withinthe battery container and also the ability to readily absorb up to percent water by weight before dissolving.

However, experimental tests have revealed that the cycle life of these dry charged batteries which contain a gel that 3O utilizes phosphoric acid as a component for immobilizing the sulphuric acid electrolyte have a shorter cycle life than cells that contain no phosphoric acid in the electrolyte. It 'is believed that the loss of cycle life is due to thephosphates in the t found to be beneficial as it restored the cycle life of the battery.

in addition. because zirconium sulfate binder for a gel container is not affected by concentrated sulphuric acid. it

5 allows for in situ preparation of the gel thus minimizing the handling of the sulfuric acid gel in its immobilized state.

This compound is also found advantageous in that the zirconium sulfate that precipitates out the phosphates has no adverse electrochemical effect on the cell reactions.

Summary of the Invention Briefly, the invention comprises placing a soluble zirconium compound in a container where it can precipitate out phosphates that would shorten the cycle life ofa secondary cell.

Description Sulfuric acid of high density can be immobilized by the addition of small amountsof inorganic compounds such as boric and phosphoric acid to form a gel. The gel dissolves completely upon activation by water to form a sulphuric acid electrolyte containing the two inorganic components.

Tests have revealed that the sulphuric acid electrolyte which has been gelled by boric and phosphoric acid had decreased the cycle life upon activation of the electrolyte by addition of water thereto.

This is unfortunate as the inorganic gelling agent provides the simplest and cheapest method ofimmobilizing a sulphuric acid electrolyte in a dry charged battery. Presently. no substitute has been found for eliminating the use of a phosphate producing compoundin the gel process that is electroelectrolyte whihh cause a portion of the positive active chemically inert and still suitable for immobilizing the material in the plates to become isolated from the cell reactions.

In the preparation of these gels that immobilize the sulphuric acid, it is preferred to use a solution of concentrated sulphuric acid in gel form.

It has been discovered that the addition of a water soluble sulphuric zirconium compound such as zirconium sulfate to the dissolved gel eliminates the undesirable decrease in Sulphuric acid Which is Slightly less than 100 percent Shh 0 cell cycling life which is attributable to the inorganic phosphuric acid'with'tl'ieTeTnaiifdEr Being vrti'rheetsacatratea sulphuric acid liquid is very corrosive and only a few materials remain unaffected by its presence. The solutions of sulphuric acid are mixed together and then allowed to gel phoric acid located in the sulphuric acid electrolyte.

1n the preparation of a typical gel container. a soluble zirconium compound such as zirconium sulphate can be either placed in the gel tray or impregnated into the gel tray in a first container which is unaffected by sulphuric acid or used as a binder for holding the tray together. The latter Next. the gel is transferred to a second container for insertion into the battery. As the sulphuric acid remains in an im; mobilized state. the second container need not be impervious to sulphuric acid. However, the handling of the gel is unuse of the zirconium as a binder is preferred as it produces a tray that is collapsible when brought into contact with water.

In the typical preparation of the tray. a non-woven desirable as it tends to reduce the firmness and Stability of asbestos is wetted in a concentrated zirconium sulfate the gel. Ideally. i t would be desirable if the gel could be prepared in situ and then inserted into a container that would collapse when the battery is activated. However, some of the container materials that could be used to prepare the gel have in a 100 percent sulfuric acid solution at 200 C. for one hour. 6

While the zirconium sulfate binder is resistant to the 100 percent concentration of sulfuric acid, it dissolves rather readily upon contact with watenThus, the container that is bound together with zirconium sulfate binde beggs to dissolve and collapse upon addition of water to the dry charged battery. This is a desirable feature as it allows the tray to collapse and thus .ttaaassssyyith ttths ba s yswaias once the battery ispl aced into operation.

In addition. it was discovered that zirconium sulfate binder in the container precipitated out the phosphates in the electrolyte after the gel had been dissolved. This was solution. The asbestos felt is formed into a suitable shape for a tray for a gel and dried at 425 C. for an hour. This produces a firm tray that is unaffected by concentrated sulphuric acid but will readily dissolve when exposed to water.

If a zirconium compound is impregnated into the tray or just placed loosely in the bottom of the container. then it is necessary to ensure thatthe proper amount ofthe zirconium compound is placed in the container. Test results reveal that placing equimolar properties of phosphoric acid and zirconium sulfate produce an effective precipitator of the phosphate from the solution. However, to ensure that all the phosphates are precipitated out, it is desirable to use a slightly larger molar concentration of the zjrconiurn compound than the phosphate affording compound.

Cyclic voltarnetric tests were conducted with lead elec trodes on the following solutions of electrolyte:

Solution A 4 molar sulphuric acid solution B 4 molar sulphuric acid+.l molar phosphoric acid C 4 molar sulphuric acid, .1 molar phosphoric acid and .13 molar of zirconium sulfate ln solution A and C the voltametric charts showed similar results but in solution B the voltametric charts showed several modifications of the pattern. Further life cycle tests confirmed that the electrolyte containing the phosphoric sulphuric acid electrolyte with the phosphoric acid and nozirconium sulfate had as much as 40 percent decrease in cycle life.

These results are given as merely illustrative of the effect of the boron phosphate on the cycle life and the improvement ofthe cycle life through the addition ofthe zirconium affording substance to the electrolyte. 1

I claim:

I. A dry charged lead acid storage battery including a positive electrode, a negative electrode, and a water activatable electrolyte precursor. said electrolyte precursor comprising sulphuric acid gelled with boron phosphate, said electrolyte precursor dis-solvable in water to form an electrolyte solution containing sulphuric acid and phosphoric acid. said storage battery further containing zirconium sulphate for reacting with said phosphoric acid to thereby precipitate zirconium phosphate from said electrolyte solution.

2. The product of claim I wherein the moles of zirconium sulphate are at least equal to the moles of phosphoric acid in the electrolyte.

3. A water activatable storage battery having improved operating characteristics comprising: a battery container; a water soluble electrolyte precursor located in said battery container; said electrolyte precursor comprising sulphuric acid solution gelled with boron phosphate so that upon the activation" of said battery by the addition of water thereto. said electrolyte precursor yields an electrolyte solution com prising sulphuric acid and phosphoric acid; and zirconium sulphate located in said container for reacting with said phosphoric acid in said electrolyte solution to thereby precipitate zirconium phosphate from said electrolyte solution and thereby prevent the phosphoric acid from adversely affecting said battery.

4. The method of making an electrolyte for a storage battery comprising the steps of:

(a) gelling sulphuric acid with boron phosphate to produce an electrolyte precursor;

(b) placing the electrolyte precursor in a storage battery;

( adding water to the electrolyte precursor to thereby dissolve the electrolyte precursor and form an electrolyte solution containing phosphoric acid; and

(d) adding zirconium sulphate to said electrolyte solution to react with the phosphoric acid to thereby precipitate zirconium phosphate out of said electrolyte solution. 

